The present invention relates to an air temperature control system in a recycling oven for cooking (both by hot air impingement and microwave energy, or by hot air impingement alone), and more particularly to such an oven which is capable of rapidly cooking food products and rapidly effecting cooking air temperature modifications.
Food service venues, such as grocery stores and convenience stores, often carry food that is typically prepared several hours before the food is purchased by the consumer. Not only does this result in substantial inventory loss if traffic is less than expected, but the food itself is often of lower quality than what might be available from a restaurant because it has been prepared well in advance of sale to the consumer and held in anticipation of sale. This reduced quality, as well as the perception of reduced quality in the minds of consumers, results in lower sales than would occur if the food quality was in line with what is cooked and immediately (or almost immediately) sold in restaurants.
Attempts to deliver "cooked to order" food of high quality within an acceptable time frame have not been entirely successful. Indeed, it is precisely this shortcoming which has prevented the creation of acceptable consumer-operated ovens or hot food vending machines (similar in size and concept to the well known soft drink vending machines) which could turn out national "fast food" chain quality food from a partially or fully automated machine.
Ovens which utilize hot air impingement as the sole method of imparting energy to the food product are not typically used in applications which require rapid cooking (e.g., less than 90 seconds) and delivery to the consumer. In such ovens, because this cooking method works from the outside inward, the impinging hot air has only a limited ability to cook the food interior, especially when the product is of substantial dimensions. This drawback illustrates one of the many disadvantages of the conventional hot air impingement oven--namely, it requires several minutes in order to cook the food product by hot air impingement alone.
Further contributing to this long cook time in an air impingement oven is the time the oven requires to adjust to new temperature settings, whether higher or lower, especially in comparison to a conventional microwave oven. Although the conventional microwave oven does not operate with "temperature" settings, its cooking intensity is rated according to the average power of the magnetron (radio frequency emitting device) over time, and regulation thereof requires a mere adjustment of the electronic controls. Such an adjustment of the electronics provides an instantaneous response by the environment within the cooking chamber of the microwave oven. In contrast, the cooking chamber in an air impingement oven is much slower to respond to adjustment, as air temperature is traditionally a function of a heat exchanger temperature. Hence, for warmer air, the heat exchanger must undergo heating until the heat exchange material thereof is sufficiently hot to condition the air passing over it. In contrast, for cooler air, the heat exchanger must sit idle until the heat exchange material thereof is sufficiently cold to cool the air passing over it. Note that this cooling process can be a slower process because of its passive nature, as opposed to the active process involved in heating the air. Therefore, cook setting adjustments in a microwave oven take effect much quicker than do adjustments, especially temperature-lowering adjustments, in a conventional air impingement oven.
The consumer-operated oven market has been largely limited to microwave ovens over the past several years, partially due to the low cost, familiarity, and fast cook times associated with such ovens. Hence, the menus offered to consumers have likewise been limited to those few food products which prepare fairly well in microwaves (e.g., baked potatoes and popcorn). In contrast to air impingement ovens, conventional microwave ovens tend to heat food outwardly from the food interior, resulting in a "synthetic" product, without browning or crisping. A hybrid oven, combining air impingement technology and microwave energy technology, can not only cook foods with proper browning and crisping, but can cook a wide variety of foods at speeds equal to or faster than conventional microwave ovens.
A satisfactory quick-cooking oven must be able to heat or cook food products--from frozen, refrigerated, or ambient temperature states--whether they are already prepared (e.g., frozen fried chicken nuggets), partially prepared (e.g., frozen "par-baked" pizza), or raw (e.g., biscuits, fish). The process must generally be completed within times that the fast food customer has become accustomed to waiting (generally less than 30-60 seconds for most single portion food products). These various pre-cook states require varying oven temperatures in order to produce quality food products. Hence, such a quick-cooking oven must be able to rapidly transition from one temperature to another, whether higher or lower, between each cook cycle or during a cook cycle. By way of an example, such an oven would permit foods requiring different cooking temperatures to be cooked in the oven in relatively rapid succession. As another example, such an oven would permit proper cooking of certain foods which require different cooking temperatures at different stages in the cooking process. (For example, optionally, certain meats are seared at a high temperature for a brief period of time prior to a normal, lower temperature cooking cycle, thereby minimizing moisture loss from the meat). Clearly, an oven which has but a single cooking temperature cannot provide the different cooking temperatures required for different foods, or the different cooking temperatures over a cook cycle required for certain other foods. At present the ovens maintain different zones of the cooking chamber at different temperatures rather than having the cooking temperature being customized and individually arranged for each particular food. Such ovens require the foods to be placed in the appropriate zone and possibly, at a later stage in the cooking process, relocated to a different zone.
It will be readily appreciated that an oven which can complete the cooking process in 30 seconds can enable food to be sold at twice the rate during peak hours than a machine which requires a minute, whether the oven is disposed in a fast food restaurant, in an ancillary foodservice location such as a convenience store, or as part of an automatic vending machine. Additionally, there is a threshold to the amount of time most consumers will wait for a food product to be delivered. Although there may be some debate as to what that threshold time limit is, it is clear that far fewer customers will knowingly wait 90 seconds for delivery of their food than will wait 30 seconds. Meeting the desires of this marginal customer group would also result in additional sales.
A hybrid oven that employs a system to rapidly achieve modified settings for the temperature of the cooking air is capable of successfully delivering "cooked to order" food of high quality within an acceptable time frame. Such an oven enables mastery of the "cooked to order" concept due to the ability of the oven to cook food products quickly, and thereby minimize the wait time required. High quality food is assured because the quick-cooking capability allows fresh ingredients to be used and, ultimately, a fresh finished product to be delivered to the consumer. High quality food is further assured by the use of two cooking methods: hot air impingement for browning and crisping the food exterior, and microwaves for cooking the food interior. Finally, such an oven assures the consumer of an appropriate time frame to deliver the high quality food product because the hybrid cooking means functions to cook all food products quickly.
Accordingly, it is an object of the present invention to provide a system, within a recycling hot air impingement oven, that is capable of rapidly modifying the air temperature, thereby enabling operations whereby a consumer can cook single entree portions of food within a limited period of time (e.g., 30 to 60 seconds), depending upon the food type, volume, and whether the food product is in a frozen, refrigerated, or ambient state.
Another object is to provide such a system that in one embodiment works in an oven using hot air impingement means alone to cook food products.
Yet another object is to provide such a system that in another embodiment works in concert with microwave cooking means to cook food products even more rapidly than with hot air impingement alone.
A further object is to provide such a system that contributes to the oven's ability to cook food products that are at least of the quality of food served at fast food restaurants.
It is another object of the present invention to provide such a system which does not diminish the oven's ability to cook a wide range of food products, one after another, but at a faster rate than without such a system.
It is a still further object to provide such a system which is safe, simple, and economical to manufacture, use, and maintain.